Electric switch



I E. MCCABE ELECTRIC SWITCH March 7, 1939.

Filed Jan. 2, 1937 2 Sheets-Sheet l lll.

Il I! THM/MAL MUM INVENTOR. E. MCC/45E ATTONEY.

March 7, 1939. l. E. MCCABE 2,149,853

ELECTRIC SWITCH Filed Jan. 2, 1937 2 Sheets-Sheet 2 INVENTOR. [RA E. MC C455 ATTORNEY.

Patented Mar. -7, 1939 UNITEDy STATES PATENT OFFICE ELECTRIC SWITCH Ira E. McCabe, Chicago, Ill. Application January 2, 1937, Serial No. 118,719

11 Claims. (CL 200-138) This invention relates to improvements in electric switches and more particularly to a further improvement in the electric switch disclosed in this applicants prior co-pending application, Serial No. 94,352, led August 5, 1936.

It is an object of this invention to construct a switch including as apart thereof a thermally actuated operating instrumentality responsive to two sources of actuating energy. It is an object to so construct the said instrumentality that when the switch is normally closed the passing of an electrical current therethrough will cause an element o1' said instrumentality to function and open the switch a predetermined time after the establishment of the circuit therethrough. It is a further object to employ radiant energy, such as rays of light, to act upon an element of said instrumentality after the establishment of the electrical circuit to prevent the functioning of said instrumentality and maintain the switch unopened as long as both sources of energy are active. It is still a further object of this invention to provide means when the absence of one source of energy results in the opening of the switch to maintain the switch open until manually reset.

A switch of this character has many applications, one, for example, is its useI in a control system for iluid fuel burners. Light responsive switches have hitherto been employed in conjunction with control systems for uid fuel burners wherein' a predetermined time is desired to permit the burner to attain its normal operating stage whereafter upon reaching that stage continued operation is permitted, but upon failure to reach normal operation within the said time a secondary thermal release switching device is actuated to render the burner inoperative. A switch constructedv in accordance with this invention when adapted to such an application is in itself a timed circuit breaker and light responsive device, thus eliminating the necessity of separate cooperating devices to accomplish the same result. An embodiment of this invention is inelusive of two elements that respond alike to changes in temperature but diifer in electrical resistance whereby the passage of an electrical current through both will cause one to deform more rapidly than the other resulting in an unequal movement between the two. It is contemplated by this invention to employ this unequal movement of two such elements to actuate the movable contact of a switch to open an electric circuit a predetermined time after the establishment of a circuit therethrough, and to employ the radiant energy of light to increase the temperature of one element by shielding the other from such rays whereby the existence of both current and light may be utilized to maintain both elements at substantially the same tempera- 6 tures and by proper arrangement the movement of the elements offset each other so that the switch remains in its normal closed position.

With these and other objects in view, reference is made to the accompanying sheets of draw- I0 ings which illustrate embodiments of this invention with the understanding that minor changes may be made without departing from the scope thereof.

In the drawings: l

Figure 1 is a view in front elevation partly in section of a preferred form of this invention.

vFigure 2 is a view in central vertical transverse section of Figure l, with parts shown in elevation.

Figure 3 is a view similar to Figure 1 of a modified form of this invention with parts broken away and partly in section.

Figure 4 is an enlarged detailed view in perspective of the operating parts shown in Figures 25 1 and 2.

Figure 51s an enlarged detailed view of a modied form of thermostatic element.

Figure 6 is a view in front elevation illustrating the form of this invention shown in Figure 1 as 30 installed in a casing and provided with means to maintain the switch in the open position.

Figure '7 is a view in section taken on the line 1 1, Figure 6 looking in the direction o1' the arrows.

Figure 8 is a diagrammatical View illustrating an application of this invention to control the operation of a uid fuel burner.

Figure 9 is an enlarged detail top plan View of a modified form of light shield in the form 40 of a reiiector.

A- convenient embodiment of this invention is to enclose the operating instrumentalities within a sealed mercury switch tube or container l, as

illustrated, in which the xed switch member is 45 inclusive of an electrode 2 passing through and sealed in the end closure 4 of the tube and terminating with its interior end submerged in a body of conducting uid 5, such as mercury, contained in a cup-like depression 6 formed in the 50 closed end of the tube opposite the closure 4 'and in which the movable switch member is in the form of an electrode 3 passing through and sealed in the end closure 4 of the tube, terminating with its interior end 1 adapted to make and break 55 closed within the tube I of -a thermally actuated operating `instrumentality. Said instrumentality is inclusive of operating elements preferably in-r cluding strips of thermal metal formed into coils 8 and 9 with the respective ends of their innermost convolutions mounted upon a shaft Il), and the respective ends of the outer convolutions secured to the fixed portion of the electrode 3 and the movable end 1, respectively, so -arranged that when the switch is out of circuit, that is before the establishment of the circuit to be controlled by the switch, the movable end 'I of the electrode 3' will be in contact with the conducting fluid 5, in'other words, the switch will be in the closed position. 4

In accordance with this invention and to construct a switch responsive to two sources of actuating energy, it is preferable to construct the operating elements of the thermally actuated instrumentality of material having the same coemcient of expansionbut offering different resistance to the passage of an electric current therethrough, so that when the circuit is established through the switch the temperature of the operating element having the greatest electrical resistance will increase more rapidly than the other and as each have the same coemcient of expansion the one having the greatest electrical resistance will distort more rapidly than the other and impart a movement to the member included in said instrumentality to break the circuit through the switch. are so constructed that the time between the closing of the circuit including the switch and' the breaking of the circuit by the operation of the switch will be constant and predetermined.

Since the coeiilcient of expansion in both elements is the same both will respond equally to changes in ambient temperature without operating the switch. Therefore if the temperature of the .element of least electrical resistance be raised independently of and at the same rate as the temoering the greatest reperature of element the establishment of the sistance is raised upon circuit including the normally closed switch, the

switch will remain in the closed position. It is therefore preferable to `construct the operating elements ofgthe thermally actuated instrumentality of thermal material which is of a nature suiciently sensitive to respond to the presence or absence of radiant energy emanating from a source of light.

By constructing the coil 9 of the desired material offering the greatest resist-ance to the passage of an electric current and then shielding saidcoil when the switch is exposed to the rays of radiant energy emanating from a source of light, and by constructing the coil 8 o f the desired material to respond to said radiant energy from a source of light and distort at the same rate as I the shielded coil 9 when the circuit to be controlled tality will fail'to actuate and will remain inoperative with the result that the closed.

It is preferable to shield coil' 9 by interposing' a disk II upon the shaft I9. between the coils 8 and 9, as shown in Figure 4, which disk may be of any material desired but is preferably ofmetal.

aieaeea I f The said operating elements is established, the operating instrumenswitch remains 'coils to increase that time.

ed form of shield in which the disk IIa is in the form of a concave reflector facing the coil 8 mounting the movable end l, whereby the said coil is affected by the direct rays of radiant energy upon one side and uponrthe other by the converging rays of energy reflected by the concave surface of the shield I IB.

As this construction is relatively delicate, external vibrations may be so transmitted to the switch as to impart a vibration to the electrode member 'I carried -thereby during movement thereof until its free end is entirely submerged within the mercury. To dampen such vibration, it is preferable to provide a U-shaped member I2 I which is mounted preferably upon a bracket I3 depending vertically from the electrode. 3 as it enters'the container I by pivoting the free ends of the member I2 thereon with the bottom section of the U resting upon the opposite side of the member l.

To prevent the cooling of the coils after the switch has been opened from again establishing the circuit therethrough, the movable contactv member 'I of the electrode 2 is provided with a rectangular curved plate I4 vof magnetic metal, such as iron, adapted to act as an armature in conjunction with a magnet I5 arranged exterior and adjacent the container I so that when the continued passage of the current through the switch moves the contact member 1 out of contact with the mercury 5 the armature I4 is brought 2l secured to the back I9 of the casing. VA coil spring 22, having one end attached to the bracket I8 and the other end to a cup 23 forming a part of a` clip embracing the well in the bottom of the tube I", normally holds the magnet I5 at the end of its travel nearest the tube I. The magnet I 5 is adjusted to hold the armature I4 with its movable contact member 1 out of contact with the mercury 5 when the movement of the coils has opened the switch. A nger 24 is provided' to extend through the back plate I9 and be secured to the reciprocating bracket I8 so that when it is desired to release the armature I4 to allow the switch to close the nger 241s manually operated to move the magnet I5 to withdraw' its eld from the armature and release the movable contact 1 to close the switch. Upon the release of the linger 24 the coil spring 22 returns the magnet to its operative position.

While the differential in expansion of the coils 8 and 9,`to provide the desired time delay inA opening the switch circuit, may be accomplished in most cases by the employment of coils having different electrical resistances it may be desirable to further slow up the movement of one of the one method of accomplishing this. By removing sections 25 of the metal 26 of one of the coils the passage of current therethrough will heat the reduced sections first and it will require the transfer of that heat, not lost by radiation, 'to4 they heavier portions whereby a longer time will be required to bring the entire coil mechanism to the temperature to produce the desired movement.

Another manner of retarding the opening of Figure-5 illustrates the switch is shown in Figure 3. l Here the movable contact member 'Ia is extended at an angle from the armature I4 to enter the mercury 5 on the sideopposite the vertical center of the tube I. In this case the armature is normally in the field of the magnet I5 and the pull of the magnetic field must be overcome before the switch is opened.

A practical application of this improved switch is illustrated in Figure 8 as employed in the control circuit of an electrically operated and controlled fluid fuel burner of the pressure type. The flame of the burning fuel issues from the end of the draft pipe 21 into the combustion chamber 28 of the furnace or heater. The motor M for supplying air and fuel is connected in circuit to the commercial source of electric current through the boiler control B, room thermostat T and control C, all of commercial form. The top of the container or tube I of this improved switch is shown in the housing 29. The housing 29 passes through the wall of the furnace or heater and opens into the combustion chamber 28. The switch tube I is mounted upon the outer closed end of the housing 29 and is so arranged that when the iiuid is ignited the rays of light from the flame of the burning fuel will pass through the open end of the housing and fall upon the switch tube I. The switch tube I is normally in closed position and is here shown connected in circuit with one coil of a repulsion relay` R, of commercial construction which controls the operation of the switch S in the motor circuit.

When the room thermostat closes the circuit the relay R is operated to start the motor to supply fuel to the burner and at the same time the circuit through the switch tube I is established. In the event the fuel is not ignited within the predetermined time for which the improved switch is set, the switch will open the circuit and the relay will open the motor switch. On the other hand, if the fuel is ignited within the predetermined time the rays of light from the flame of the burning fuel will act upon the unshielded coil 8 of the improved switch and equalize the movement of both coils 8 and 9 so that the cur-- rent will continue to pass through the `switch and relay to maintain the motor circuit closed.

It is to be understood that the use of this particular switch is of wide application'and is not limited to the use cited as an example. Likewise this invention is not limited to the exact construction illustrated, which merely forms a convenient embodiment, as the novel combination of the use of the response to electric energy and' radiant energy of the operating instrumentality need not be enclosed in a sealed container nor the switch circuit controlled through a mercury contact.

What I claim is:

1. An'electrical switch having a fixed contact and a movable contact to 4open and close the switch, means to normally maintain the switch closed having an instrumentality included in the movable contact provided with means responsive to the passage of an electrical current therethrough to impart movement to said contact to open said switch, and means responsive to radiant energy to prevent said movement of said contact.

2. The structure of claim 1 wherein said instrumentality includes two thermally responsive elements having the same coeiiicient of expansion but oifering different degrees of resistance .to the passage of an electrical current.

3. The structure of claim 1 wherein said instrumentalities include two thermally responsive elements having the same coefficient of expansion but offering different degrees of resistance to passage of an electrical current and wherein said last named means includes means shielding the element of greater resistance from rays of `radiant energy emanating from a source oi' light while exposing the other element thereto.

4. A mercury tube electric switch including a body of mercury therein, two electrodes sealed in the walls thereof, one electrode arranged to enter into and maintain contact with the body of mercury, the other arranged to normally enter into said body of mercury to closeV the switch, said latter electrode including means actuated by heat generated by the resistance to the passage of the current therethrough to move said electrode out of contact with the mercury to open the switch a predetermined time after the establishment of the circuit therethrough, additional means to coact with said first means to maintain the movable electrode in contact with the said body of mercury actuated by heat oi.' radiant energy of light, while shielding the first means therefrom, whereby the heat of electrical resistance in the rst means is equalized by radiant heat in the additional means, said coacting means having the same coeflicient of expansion, including means retarding the opening of the switch upon the initial movement of said first means, said retarding means consisting of an external magnetic force adapted to include in the magnetic field thereof, to maintain a closed circuit, a magnetizable element forming a part of the movable electrode.

5. A normally closed electrical switch having a movable contact arm provided with means actuated bythe passage of an electric current through the switch to impart movement to said arm to open said switch, said means including two counter-acting coils of thermal metal of the same coeflicient of expansion but offering different degrees of resistance to the passage of the current therethrough and sufiiciently sensitive to respond to the presence or absence of rays of radiant energy. emanating from a source of light, and a light shield interposed between said coils, whereby upon establishing a circuit through said switch and simultaneously exposing the coil of least resistance to said rays of light with the other coil shielded therefrom, the expansion of the shielded coil is equalized and the switch remains closed.

6. A mercury tube switch including a body of mercury therein, two electrodes sealed in the walls thereof, one electrode arranged to enter into and maintain contact with the body of mercury, the other arranged to normally enter into said body of mercury to close the switch, said latter electrode having interposed therein two counter-acting coils of thermal metal of the same coefficient of expansion but offering diiierent degrees of resistance to the passage of the current therethrough, a common shaft mounting said coils with the outer convolution of one coil secured to the said electrode and the outer convolution of the other secured to the portion of the electrode adapted to be moved into and out of contact with the mercury, said coils actuated by the establishment of a circuit through the switch to move said electrode to open said switch, said movable electrode provided with an armature, and a magnetic force'exterior of said switch tube normally attracting said armature against the initial movement o: the coils to maintain the movable electrode in contact with said mercury so upon the opening of the switch circuit by movement of the electrode the armature is sulciently removed from the effective magnetizable area as to prevent the reclosing of the switch upon cooling of the coils.

7. A mercury tube switch including a body of mercury therein, two electrodes sealed in the walls thereof, one electrode arranged to enter into and maintain contact with the body of mercury, the other arranged to normally enter into said. body of mercury to close the switch, said latter electrode having interposed therein two counter-acting coils of thermal metal of the same coemcient of expansion but offering different degrees of resistance to the passage of the current therethrough, a common shaft mounting said coils with the outer convolution of one coil secured to the said electrode and the outer convolution of the other secured to the portion of the electrode normally in contact with the said mercury, said coils actuated by the establishment of a circuit through the switch to move said electrode to open said switch, said movable electrode provided with an armature,

and a magnetic force exterior of said switch tube so the movement of the electrode to lopen the switch lbrings said armature within the magnetic eld of the said force to prevent the closing of the switch upon the cooling of the coils. d

8. 'Ihe structure of claim 5 wherein the coil offering the greatest resistance to the passage of the circuit therethrough is reduced in cross-sectional area at points spaced apart throughout the length of its convolutions to thereby retard the expansion thereof.

9. A mercury tube electric switch including a body of mercury therein, two electrodes sealed in the walls thereof, one electrode arranged to enter into and maintain contact with the body of mercury, the other arranged to normally enter into said body of mercury to close the switch, said latter electrode including means actuated by heat generated by the resistance to the passage of the current therethrough to move said electrode out of contact with the mercury-"to open the switch a predetermined time after the establishment of the circuit therethrough, and wherein said means includes additional means to co-act with said rst means to maintainthe movablel electrode in contact with the said body of mercury actuated by heat of radiant energy of light, while shielding the rst means therefrom, whereby the heat of electrical resistance in the rst means is equalized by radiant heat in the additional means, said co-acting` means having the same coefcient of expansion.

l 10. A mercury tube electric switch including a body of mercury therein, two electrodes sealed in the walls thereof, one electrode arranged to enter into and maintain contact with the body of mercury, the other arranged to normally enter into said body of mercury to close the switch, said latter electrode including means actuated by heat generated by the resistance to the passage of the current therethrough to move said electrode out oi contact with the mercury to open the switch a predetermined time after the establishment of the circuit therethrough, and wherein the said means includes the arrangement intermediate the ends of the second electrode, of a shaft and coils of thermal metal attached at their ends to the respective ends of said shaft and at their outer ends to the respective sections of said electrode, said coils so adapted as to expand unequally upon the establishment of a circuit therethrough.`

11. A mercury tube electric switch including a body of mercury therein, two electrodes sealed in the walls thereof, one electrode arranged to enter into and maintain contact with the body of mercury, the other arranged to normally enter into said body `of mercury to close the switch, said latter electrode including means actuated by heat generated by the resistance to the passage of the current therethrough to move said electrode out of contact with the mercury to open the switch a predetermined time after the l establishment of the circuit therethrough, and wherein said meansincludes additional means actuated by heat of radiant energy of light to co-act with said rst means to equalize the heat of electrical resistance therein to maintain the movable electrode in contact with said body of mercury, and wherein said additional means includes the provision upon the shaft of means shielding one of the coils from the rays of light.

I RA E. McCABE. 

